Facebook shares have fallen to a new low as the year's biggest flotation continued its disastrous decline.

The social network dropped 17% to $22.28 as investors logged out following its first set of results as a public company. Revenues of $1.18bn ($750m) matched analysts expectations, but Wall Street was worried about the growing number of mobile users - now thought to account for 57% of the business - since the company has so far found it difficult to make money from advertising on these accounts.

Its shares had already come under pressure on Thursday after poor results from gaming group Zynga, which accounts for 12% of Facebook's revenues.

The company floated at $35 a share in May, but it has been on the slide more or less ever since with many analysts saying they had been priced too dearly. But analysts at Morgan Stanley, the lead bank behind the much-hyped float, repeated their $38 price target although they admitted:

While we believe Facebook will lead the market in mobile ad targeting, agency and brand transitions to mobile may take longer than expected. Facebook must find the right balance of information sharing that will enable it to deliver favorable ad targeting, but not antagonize users or legislators who desire greater levels of privacy.

However the shares could come under further pressure in the run up to 19 August, when some early investors will be able to sell their shares, potentially flooding the market with stock.